Chemical sensitization of photographic emulsions



Patented Aug. 15, 1950 7 CHEMICAL SENSITIZATION OF PHOTO- i GRAPHIC EMULSIONS Wesley G. Lowe and Jean E. Jones, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application November 18, 1948, Serial No. 60,818

17 Claims.

Thisinvention relates to photographic emulsions and more particularly to chemical sensitizers therefor.

It is well known that silver halide emulsions may be chemically sensitized with a variety of materials so as to increase the speed and generally the gamma of the emulsions as opposed to optical sensitizing in which the optical range of sensitivity is increased. Depending upon the materials and methods employed, it is generally regarded that chemical sensitization results in either the formation of silver sulfide on the surface of the silver halide crystal or results in the formation of small amounts of silver from the reduction of silver halide, which effect may be in addition to the former effect sometimes known as sulfur sensitizing. The present invention is concerned primarily with chemical sensitization apparently of the latter type.

-Among the materials previously proposed for augmenting emulsion sensitivity may be mentioned basic compounds such as ammonia and certain aromatic and aliphatic amines such as triethylaniine and triethanolamine; whereas other amines such as propylamylhexylamine are said to have no eifect upon emulsion sensitivity. Similarly, .we have found that simple polyamines such as ethylene diamine are not effective chemical sensitizers for silver halide emulsions. On the'other hand, we have discovered certain polyamine compounds similar in structure to ethylene diamine which surprisingly are powerful sensitizers for silver halide emulsions.

. One object of our invention is to provide chemically sensitized silver halide emulsions of enhanced sensitivity. Another object is to provide novel chemical sensitizing agents for photographic emulsions. Another object is to provide hanced by means of both sulfur sensitizers and the novel sensitizers of our invention. A further sion layers of polyamine compounds such as diethylene triamine, triethylene tetramine or tetraethylene pentamine, tetrapropylene pentamine, and the like. The compounds have the general structure where n is a positive integer from'one to five, preferably one to three, and R is an alkylene chain of from two to four carbon atoms, preferably two carbon atoms. The three first-mentioned polyamines are particularly desirable not only because of the speed increases they eifect, but also because their synthesis is relatively simple compared to polyamines of higher molecular weight, therefore they are more readily available in a high degree of purity.

The novel sensitizers are incorporated in the emulsions at any stage in their preparation but referably before digestion is complete. Generally, in order to obtain the optimum sensitizing effect, we heat the emulsion after addition of the sensitizing agent. The sensitizers may be used in conjunction with other chemical and optical sensitizers such as the well known sulfur sensitizin compounds such as disclosed in Sheppard U. S.'Patents 1,574,944, granted March 2, 1926, and 1,623,499, granted April 5, 1927. Our novel sensitizers may be employed before, after or simultaneously with sulfur sensitizing. Also our novel sensitizers are useful with a variety of emulsions, producing pronounced speed increases in either negative or positive types of emulsions.

Our invention will now be illustrated by reference to the following specific examples.

Example 1 Several cc. samples of a high speed bromoiodide positive type of emulsion, each containing silver halide obtained from 20 grams of silver nitrate andpeptized with a gelatin derivative by the process of the Lowe et a1. U. S. application Serial No. 768,478, filed August 13, 1947, were adjusted to a pH of 6.0 and heated for 30 minutes at 50 C. with four mg. respectively of the diethylene triamine, triethylene tetramine and tetraethylene pentamine added in aqueous solution adjusted to pH 6.0. After this, each sample was added to 400 cc. of a five per cent gelatin solution and coated on a support and dried in the usual manner. After exposure of the emul- 3 4 sion coatings in an Eastman Type 23 Sensitomethe emulsions are shown in the table (samples ter, the samples were developed in a developer J, K and L). of the following composition: Similar speed increases were obtained by treat- Water 1 liter merit of negative emulsions before or after sulfur sensitizing, with the other polyamines and salts thereof forming a part of our invention.

p-Methylaminophenol sulfate, 0.3 gram Hydroquinone, 6.0 grams Sodium sulfite (dry), 38.0 grams SOdillIl'l bisulfite, 1.2 grams Sample Chemical Sensitizer Fog Gamma Sodium carbonate (dry), 19.0 grams Potassium bromide, 0.9 gram 0.01 L 9 43 Citric acid, 0.7 gram 0.01 2.1 0. 71 0.01 2.4 0.98 The exposed and processed emulsion coatings 8-8; A containing the polyamine sensitizers were found M 5 to have increased in speed as shown in the table 8-8; 3%: following (samples A to D). 2B Sensitometers 1 1 1 0.13 1.50 650 me described in J. Soc. Mot. Pict. Eng. 17 (1931) Sulfur ra mg. TEPmm 0'11 1'59 920 Sulfur and.2 mg. TEP 0.13 1.46 960 Example 2 20 Diethylene triamine. 100 cc. samples of the same type of positive mmthymnetemmine emulsion used in the above examples were sul- Ietraethylene pent-amine.

Sens itiZed with f tilioureaj as It will be apparent from consideration of the scrlbed g Lowe et g g i z above data that the polyamines are effective in P each g or 3 t i f producing large speed increases in emulsions 5 Wlth mm net ylepe ramme 01 treated therewith, in most cases the increases tetraethylene pentamine added in -aqu with sulfur sensitized emulsions being considerfg i f f 'g Wlth g g T ably greater than obtained from the sensitizing ZfS g i figii g? z g gg effects of the individual sensitizers when used a a e 1S alone.

resultant coatings are tabulated in the table fol- In the manner of the above examples, other lowmg ga fi i g to It 3 types of silver halide emulsions may be treated P ajpparen 5 e a apprecia; f with our novel sensitizing agents alone or in conincieases hayv been eifected by sensitizing Jhe junction with other chemical or optical sensi emulsions m the manner descnbed' tizers. The amount of sensitizing agent may,

Example 3 depending upon the type of emulsion used, vary somewhat from the optimum amounts employed in the above examples, one-fifth to five times as much sensitizing agent producing emulsions of 40 useful sensitivity. As is apparent, less heating is usually required when the larger amounts are employed and conversely when using the smaller quantities of sensitizing agent.

It will be noted in the above examples that the sensitizing of the emulsions with the novel compounds was efiected at relatively low pH. This is not a limitation of our invention but more an advantage thereof since we are able to suppress sulfur sensitivity by lowering the pH of the emul- 169 cc. samples of a high speed bromo-iodide negative type of emulsion containing silver halide from 26 grams of silver nitrate and 32 grams of gelatin were each diluted with water to 460 cc. and the pH adjusted to 6.4:. To one sample was added one mg. of tetraethylene pentamine in aqueous solution adjusted to pH 7.0 with acetic acid. The emulsion and control sample were heated at C. for one hour, then coated and 45 dried as usual. The coatings were exposed on an Eastman Type 13 Sensitometer and developed four minutes in a developer of the following composition: 1

5O sion and since the novel sensitizers are so active, W ablbut 0? C), 500 further sensitization takes place even substan- D- y a op fll S grams tially below the neutral point when they are Sodium sulfite, desiccated, 96.0grams dd d to th l i l i grams The novel sensitizers may, in general, be em- Sodium car na e, de i a 4 ram ployed in .hydrophilic colloid emulsion vehicles;

Potassium bromide, 5.0 grams for example, gelatin, polyvinyl alcohol, partially Cold water to .make, 1.0 liter hydrolyzed cellulose esters, such as cellulose ace- The character of the resultant emulsion is We and -1 mm of polyvinyl h he tabulated in the table following (samples I and sensitizers are Suitable for the well known types J). Comparable results were obt in d h th ofsilyer chloride, silver bromide and silver iodide pentamine was heated with silver halide grains emulSiOnS emulsions Containing m x ur s o befor addition of the gelatin. these halides, containing the usual emulsion ad- Emmple 4 denda such as antifoggan'ts, spreading agents,

coupler compounds, etc. Such emulsions are suitn the Ina-111161 0f EXample 450 0 Samples of 5 able to use in forniingsingle as well as multilayer the above negative type of emulsion containing film useful in color photography which custogelatin were first sulfur sensitized by heating marily include on a support two or more vemulwith a sulfur sensitizing agent at 59 C. for 20 sion layers sensitized to different regions of the minutes, then cooled to 40 C. and one or two visible spectrum .and may or may not contain mg. additions of the tetraethylene pentamine coupler compounds. According 'to our invention solution were added followed by heating at 50 C such color films carry at least one emulsion layer for 20 minutes. The samples were coated and containing a sulfide sensitizing agentof our .indried as usual, exposed in an Eastman Type 13 vention.

Sensitometer and developed 4 minutes in the de- Our invention having beendescribed, we would veloper of Example 3. The characteristics of a have it understood that the preceding description is by way of example only and that our invention is to be taken as limited only by the scope of the appended claims.

What we claim is:

l. A light-sensitive photographic emulsion comprising silver halide and a polyamine sensitizing agent having the general formula:

HzN (RNH) nRNHZ wherein R. is an alkylene chain having from 2-4 carbon atoms and n is a positive integer of from 1-5.

2. A light-sensitive photographic emulsion comprising silver halide and a polyamine sensitizing agent selected from the group consisting of diethylene triamine, triethylene tetramine, tetraethylene pentamine, and their watersoluble salts of non-desensitizing acids.

3. A light-sensitive photographic emulsion comprising silver halide and triethylene tetramine as a sensitizing agent.

4. A light-sensitive photographic emulsion comprising silver halide and tetraethylene pentamine as a sensitizing agent.

5. A light-sensitive photographic emulsion comprising silver halide and diethylene triamine as a sensitizing agent.

6. A light-sensitive photographic emulsion comprising sulfur sensitized silver halide and triethylene tetramine as an additional sensitizing agent.

7. A light-sensitive photographic emulsion comprising sulfur sensitized silver halide and tetraethylene pentamine as an additional sensitizing agent.

8. A light-sensitive photographic emulsion comprising sulfur sensitized silver halide and diethylene triamine as an additional sensitizing agent.

9. The method of increasing the speed of a photographic silver halide emulsion which comprises imparting sulfur sensitivity to said emul-. sion and effecting a further increase in sensitivity by digestion of said emulsion in the presence of triethylene tetramine.

10. The method of increasing the speed of a photographic silver halide emulsion which comprises imparting sulfur sensitivity to said emulsion and effecting a further increase in sensitivity by digestion of said emulsion in the presence of tetraethylene pentamine.

11. The method of increasing the speed of a photographic silver halide emulsion which comprises inparting sulfur sensitivity to said emulsion and effecting a further increase in sensitivity by digestion ofsaid emulsion in the presence of diethylene triamine.

12. The method of sensitizing a photographic silver halide emulsion which comprises digesting said emulsion in the presence of a sulfur sensitizing agent and a polyamine sensitizing agent having the general formula:

HzN (RNH) nRNHZ wherein R is an alkylene chain having from 2-4 comprising sulfur-sensitized silver halide and as an additional sensitizing agent a polyamine having the general formula I-IzN (RNH) nRNHz wherein R is an alkylene chain having from 2 to 4 carbon atoms and n is a positive integer of from 1 to 5.

17. The method of increasing the speed of a photographic silver halide emulsion which comprises imparting sulfur sensitivity to said emulsion, adjusting the pH of said emulsion to below neutrality, and eifecting a further increase in sensitivity by digestion of said emulsion in the presence of a sensitizing agent having the general formula:

H2N RNH nRNHZ wherein R is an alkylene chain having from 2 to 4 carbon atoms and n is a positive integer of from 1 to 5.

WESLEY G. LOWE. JEAN E. JONES.

REFERENCES CITED The following references are of record in the file of this patent:

FOREIGN PATENTS Country Date Great Britain Nov. 21, 1938 Number Sulfur and TEP;

Certificate of Correction Patent No. 2,518,698 -August 15, 1950 WESLEY G. LOWE ET AL. It is hereby certified that error appears in the printed specification of the above numbered patent requiringpprrectmn as follows: 7

Column 4, line 15, in the table, secohd olfimn thereof, for do s read and that the said Letters Patent should-be read as corrected sthot'e, soJthat the same 7 W may conform to the record of the ease in the Patent Ofiice. s

Signed and sealed this 7th day of November, A. D. 1950.

THOMAS "FQMURPHY,

Assistant Gammissz'oner of Patents. 

1. A LIGHT-SENSITIVE PHOTOGRAPH EMULSION COMPRISING SILVER HALIDE AND A POLYAMINE SENSITIZING AGENT HAVING THE GENERAL FORMULA: 